1. Field of the Invention
The present invention relates to polymer blends which have a combination of both elastic and thermoplastic properties and, more particularly, relates to dynamically vulcanized alloys (DVAs) wherein an EPDM rubber is dispersed into a thermoplastic ethylene copolymer resin and subsequently vulcanized by dynamic vulcanization techniques utilizing a non-peroxide curing system. Compositions of the present invention when fully cured manifest unexpected resiliency characteristics as well as improved heat shrinkability.
2. Prior Art
Dynamic vulcanization techniques for producing polymer compositions having both elastic and thermoplastic properties are described by Gessler and Haslett in U.S. Pat. No. 3,037,954 wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and subsequently cured while continuously mixing and shearing the polymer blend. The result is a micro-gel dispersion of cured rubber in an uncured matrix of resinous thermoplastic polymer.
Dynamically cured thermoplastic olefin ("TPO") compositions wherein the elastomeric material is an EPDM rubber are well known. For example, U.S. Pat. No. 4,130,535 discloses fully cured TPO compositions wherein the rubber component is an ethylene-propylene terpolymer (EPDM) and the thermoplastic polyolefin resin is polypropylene. Ethylene copolymer resins are not disclosed. The curative system may include a peroxide, azide or accelerated sulfur curative system.
U.S. Pat. No. 4,311,628 discloses fully cured TPO compositions wherein the rubber component is an EPDM rubber and the demonstrated thermoplastic polyolefin resin is polypropylene. Improved compression set is reportedly achieved utilizing a phenolic curative which includes a phenolic curing resin and a cure activator such as zinc oxide. Ethylene copolymer thermoplastic resins are not disclosed.
Other patents which disclose a least partially cured EPDM-containing compositions include U.S. Pat. Nos. 4,409,365; 4,350,795; 4,212,787; 4,202,801; 4,087,485; 3,904,470; 3,862,106; 3,806,558; and 3,758,643; and JP 8145741.
TPO compositions wherein the thermoplastic polymer resin is an ethylene copolymer resin utilized in the present invention are also well known. For example, U.S. Pat. No. 4,639,487 discloses fully cured TPO compositions wherein the thermoplastic polyolefin resin is an ethylene-vinyl ester copolymer or an ethylene-alkyl acrylate copolymer and a rubber component selected from a group of rubber materials which includes butyl, halogenated butyl, EPDM, polyisoprene, polychloroprene, SBR, nitrile and chlorosulfonated polyethylene rubbers. The curative system can be any non-peroxide curing system.
Other patents which disclose at least partially cured TPOs containing the ethylene copolymer resins utilized in the present invention include U.S. Pat. Nos. 4,350,795 and 4,212,787; and JP 8145741.